Brush retaining means for an electric motor



March 18, 1969 w. R. LEAVITT 3,433,989

. BRUSH RETAINING MEANS FOR AN ELECTRIC MOTOR Filed Au 10. 1966INVENTOR. WILLIAM R. LEAVITT flaw 14.

ATTOR Y United States Patent Claims ABSTRACT OF THE DISCLOSURE An easilyreplaced brush for electric motors which employs a bowed spring memberhaving a resilient, elongated, leaf member depending therefrom. Thespring member clips into a plastic housing arranged to cause the springmember to assume a bowed configuration.

This invention relates generally to dynamoelectric machines and inparticular to removable means for holding the brushes thereof.

In dynamoelectric machines, such as an electric motor, springs are usedto hold the electrically conductive brushes against the commutator. Themost common form of holding means for the brush is a coil springdisposed radially to the axis of the motor shaft and commutator. In thepast, leaf springs have also been used to resiliently support thebrushes.

The present invention is particularly directed to improved springs ofthe leaf type. The brushes themselves are secured to a tab that isresiliently integral with the body of the leaf spring. Means areprovided on two opposed sides of the housing for easily inserting theleaf springs whereby the face of the brushes is in tangential contactwith the rotating commutator of the motor.

The construction of the present invention, to be described in detailhereniafter, provides several important advantages. The brush holdersare easily manufactured by a stamping operation from beryllium copper,and in contrast to the prior art there is a bare minimum of wastematerial. Because the brush holder is loaded upon insertion, the brushitself will apply a uniform force against the commutator through acomposite spring action. The brush holder is characterized by a morebenign permanent set and, in addition, has no highly stressed areas.Accordingly, a longer life is available and a greater deflection ispossible without a permanent set.

It has been found that at 40,000 rpm, for example, brushes of otherdesigns will produce sharp spikes on an oscilloscope. The patternobserved is a result of spring bounce. The construction of the presentinvention substantially reduces this undesirtable characteristic. Thebrush itself may be rigidly secured to the resilient brush block tab byany one of several means. For example, the brush may be staked orintegral gripping tabs may be provided.

Slot car motors are examples of devices that can advantageously employthe removable brush block of this invention. These motors are hobbytrade items and accordingly, a low initial cost and ease of repair areessential. Replacement of the brushes by the user himself and not askilled mechanic is very important. The motors used with slot carsoperate at high rates of rotation, typically 20,000 r.p.m., and brushwear is severe. Even higher rotational rates are desirable but generallyhave not been available with low cost motors. By way of contrast, thepresent invention provides a motor that successfully operates in the40,000 r.p.m. range.

Accordingly, it is an object of this invention to provide improved brushblock mounting means for a low cost, dynamoelectric machine.

It is another object of this invention to provide an improved brushmounting member that is easily manufactured with a minimum of wastematerial.

A further object of this invention is to provide brush mounting meansthat may readily be inserted and removed from the motor housing.

Still another object is to provide improved brush mounting means asdescribed above that minimizes the spring bounce characteristic.

A further object of this invention is to provide improved brush mountingmeans having a long life while exhibiting uniform springcharacteristics.

A particular object of this invention is to provide an improved leafspring type brush holder for a dynamoelectric machine.

Another object is to provide a holder having a cantilevered resilienttab arranged to hold the commutator brush of a dynamoelectric machine.

Yet another object of this invention is to provide a brush holder of theaforementioned type wherein the body of the holder is resilient.

A feature of this invention is that the leaf spring type brush holder isinserted in the housing of the dynamoelectric machine in a loadedcondition and is held therein at the ends of the holder.

A different feature of this invention is that the body of the holder isbowed and spans the commutator While an integral brush holding tab issubstantially tangential to the commutator.

A particular advantage of this invention is that the improved brushholder permits the manufacture of an improved low cost motor capable ofattaining high rotational rates, the motor being further characterizedby a greater ease of brush replacement than was available with prior artdevices.

These and other features, objects and advantages of the invention will,in part, be pointed out with particularity, and will, in part, becomeobvious from the following more detailed description of the inventiontaken in conjunction with the accompanying drawing which forms anintegral part thereof.

In the various figures of the drawing like reference charactersdesignate like parts.

In the drawing:

FIG. 1 is a side elevational view of a typical motor employing the brushmounting means of this invention;

FIG. 2 is an enlarged plan view of the brush mounting member of thisinvention;

FIG. 3 is a longitudinal sectional view taken along line 3-3 of FIG. 2;

FIG. 3A is a fragmentary side elevational view partly in section,illustrating an alternative configuration for the brush holding member;

FIG. 4 is a sectional end'elevational view taken along line 4-4 of FIG.1 showing the relationship of the brush mounting means to the motor endcap and commutator; and

FIG. 5 is a fragmentary elevational view that is typical of the abutmentof both brush holder ends and the slots in the motor end cap in whichthey are contained.

Referring now to FIG. 1 of the drawing, motor 10 is comprised of ahousing 12 and an end cap 14 that is made of an insulating material. Aconvenient way of securing the end cap to the housing is by means of apair of diametrically opposed locking tabs 15 integral with the housing.Tabs 15 snap into oppositely facing recesses in the end cap.

Motor 10 also includes a commutator 16 mounted on a shaft 17 rotatablewithin the housing. Although not specifically illustrated, the shaft iscarried by bearings. A stator is also included and is comprised of apermanent magnet. These components are all conventional in the motor artand will not be described in great detail. A brush 18, made of asuitable, electrically conductive material such as a molded carboncomposition, is secured to each of the two brush holders and 20 whichwill be described subsequently. The brushes are positioned to wipe thecommutator 16.

The configuration of the brush holders is clearly illustrated in FIG. 2and FIG. 3. Therein it will be seen that the body 22 of the holder issubstantially rectangular and is provided with opposite ends 24 and 26.By way of example, the brush holder may be stamped from half hardberyllium copper which is subsequently heat treated andelectro-tin-plated. The thickness of the holder may vary in accordancewith the application.

Although solder tabs may be placed at various locations on the body ofthe brush holder, in the embodiment illustrated, end 24 is provided withan aperture for this purpose. End 24 is also provided with a reducedcross section defined by two opposed edge notches 32 which serve as aheat dam when a wire is soldered in aperture 30. At the opposite end 26of the brush holder, an installation hole 34 and a pair of removalnotches 36 are also included, the function of which will be explainedhereinafter.

The central portion of the body of the brush holder has a U-shaped notch38 stamped therein, thus defining a resilient spring finger 40 that ishinged along a theoretical line X. The free end 42 of the spring fingeris bent away from the body of the brush holder (FIG. 3) in a directiontowards the commutator and includes an opening 44 in which brush 18 maybe secured. Alternatively, as shown in FIG. 3A, the free end 42' ofspring finger 40 may have a pair of opposed tabs 46 integrally formedthereon. In the alternative embodiment, the brush would be capturedbetween the tabs. Still another method of securing the brush (notillustrated) is by staking or riveting the brush to the spring finger ofthe holder.

The installed brush and brush holder may be seen in relationship to thecommutator in FIG. 4. The remaining internal structure of the motor hasbeen omitted for clarity. This conventional structure forms no part ofthe present invention.

In the embodiment illustrated, the length dimension d (FIG. 2) of thebody of the holder is 0.735 inch, whereas the spaces s (FIG. 4) betweenshoulder 50, 52 and 50', 52' in the motor housing is 0.720 inch. Thesedimensions are given by way of illustration only and are not intended tobe limiting. It will be seen then that because the body dimension isgreater than the space in which it is contained, the body will be bowedinwardly. Thus the bent end of the spring finger as well as the brushwill be tangential to the surface of the commutator.

End cap 14, in addition to openings 54, 54' between the shoulders, isalso provided with slots 56, 58 and 56', 58'. Ends 24 of the two brushholders are dimensioned to be received in slots 56 and 56 while somewhatnarrower ends 26 of the brush holder are dimensioned to be received inslots 58 and 58. The brush holders are inserted in their respectiveslots, one end at a time through openings 54 and 54. After the first endis inserted in its slot the holder is flexed to permit the opposite endto be inserted in the other slot. End faces 60 and 62 (FIG. 2) bearagainst shoulders 50 52, respectively (FIG. 4), to prevent the holderfrom relaxing. This is also shown in FIG. 5.

The foregoing assembly procedure is simplified by inserting a suitabletool in installation hole 34. To take out the brush holder anotherspanner type tool is used in conjunction with removal notches 36. Aforce is applied against the notches forcing end 26 out of its slot.With the brush holder in place, a lead wire may be soldered to end 24.When the holder is to be removed for replace ment of the brushes, theend 24 is cut off and the holder is discarded and replaced by a new one.The holder is sufiiciently inexpensive to permit its mutilation.

The brush holder hereinabove described is easily and inexpensivelymanufactured. In addition, the composite spring action provides foruniform brush tension and greater deflection without imparting apermanent set to the brush holder. Various means have been included formounting the brush on the holder. Further, the holder is easilyinstalled, securely held in a loaded condition, and may readily beremoved when the brush must be replaced.

Having thus disclosed the best embodiment of the invention presentlycontemplated, it is to be understood that various changes andmodifications may be made by those skilled in the art without departingfrom the spirit of the invention.

What is claimed is:

1. In a dynamoelectric machine having a slotted, apertured housing and acommutator rotatable together with a shaft mounted in the housing,improved means to hold a conductive brush in wiping contact with thecommutator comprising:

(a) a substantially rectangular spring member insertable through thehousing aperture and having first and second end portions dimensioned tobe received in the housing slots whereby the central portion of saidspring member is bowed inwardly towards the axis of the shaft;

(b) a resilient, elongated leaf member integral at one end with saidspring member intermediate said first and second ends thereof, theopposite, free end of said leaf member being disposed in proximity tothe commutator surface; and

(c) retaining means to secure a conductive brush to the free end of saidleaf member whereby the brush is in tangential, wiping contact with thecommutator surface.

2. The device in accordance with claim 1 including stop means integralwith said spring member, said stop means being arranged to maintain thecentral portion of said spring member in an inwardly bowed condition.

3. The device in accordance with claim 1 wherein one of said endportions includes a reduced cross section defining a heat dam.

4. The device in accordance with claim 1 wherein said spring member andsaid leaf member are one piece, said leaf member being hingedlyconnected to said spring member along one edge and spaced therefrom onthe three remaining edges thereof.

5. The device in accordance with claim 1 wherein said retaining meanscomprises a pair of spaced tabs formed integrally with the free end ofsaid leaf member, said tabs being dimensioned to securely receive thebrush.

References Cited UNITED STATES PATENTS 3,311,763 3/1967 Jepson et a1.310-239 XR 3,296,473 1/1967 Malbuchi 310-239 3,045,137 7/1962 Simmons eta1. 310-239 XR 2,842,692 7/1958 Johnson et a1. 310-246 XR MILTON D.HIRSHFIELD, Primary Examiner.

M. O. BUDD, Assistant Examiner.

